Theme Development Enhancements In WordPress 3.8

Some news on recent changes for WordPress 3.8 that make theme development even easier:

Post Formats

From 3.8 onwards, theme developers will be able to check if a post has any post format associated by checking has_post_format() without passing an argument:

// Does the post have any format assigned to it?
has_post_format();
// Does the post have this specific format assigned to it?
has_post_format( 'aside' );
// Does the post have any of these formats assigned to it?
has_post_format( array( 'aside', 'image', ) );

Background Images

Additionally, it is now possible to be more specific about a theme’s custom background support. You can now specify default-repeat, default-position-x, and default-attachment arguments for background images. This is the full array of defaults when registering theme support now:

Miscellaneous

With the improved theme experience in the Appearance menu, WordPress can accommodate for even bigger screenshot sizes of your theme, the new standard size is now 880x660px!

If you have themes in the WordPress.org repository or plan to release a theme there (you should!), these three tags will be available to classify your theme appropriately: responsive-layout, fluid-layout, fixed-layout.
They replace fluid-width and fixed-width, to make the terms broader and match web design terminology better. You can also classify your theme as accessibility-ready – if it is.